elements of renal function Flashcards
What is the function of the kidney?
regulate the volume and composition of the extracellular fluid
what does the cortex of the kidney contain?
it contains the renal corpuscles- the glomerular capillaries and bowman’s capsules
What does the outer medulla of the kidney contain?
outer medulla contains the Thich ascending limb of Henle’s loop and the Collecting ducts
what does the inner medulla of the kidney contain?
inner medulla contains the thick and thin ascending loops of Henle and the collecting ducts
how many nephrons does each kidney contain?
1 million nephrons in each kidney
what is the tubular filtrate?
as blood flows through the glomerulus, a fraction of the solutes and water is filtered across the capillary walls into the tubule - this is the tubular filtrate
what portion of the nephron absorbs the most water?
proximal tubule
what percent of cardiac output goes through the kidneys?
25% of the cardiac output flow through the kidneys
Where does the blood supply to the kidneys go to?
90% goes to the cortex
10% goes to the medulla - in the environment around the loop of henle, must be salty to allow for water reabsorption. If there is too much blood flow in this area, it will wipe away the salty interstition
What mechanisms are responsible for the autoregulation of RBF and GFR?
1) myogenic mechanism: responds to arterial pressure changes
2) tubuloglomerular feedback mechanism: responds to [NaCl]
What steps are involved in the myogenic response to increased pressure?
- increased arterial pressure
- pressure in afferent arteriole increases
- stretch of afferent arteriolar wall
- reflex contraction of muscle in wall of afferent arteriole (blood pressure goes up and stretches the afferent arteriole to maintain pressure there)
- afferent arteriolar resistance increases
- Renal blood flow remains constant
Describe the process of tubuloglomrular feedback
when the rate of fluid flow through the tubules changes (resulting fro a change in RBF and GFR) a signal originating in the macula densa of the ascending limb of the loop of henle responding to [NaCl] cuases a change in afferent arteriolar tone
- presure in afferent arteriole increases
- RBF and GFR increase
- Tubular flow rate increases
- amount of NaCl delivered/min to macula desa increases
- increased NaCl reabsorption by macula densa cells
- this leads to increased afferent arteriolar reistance
What is the Macula Densa?
region of specialized epithelial cells in thick ascending limb of loop of henle - in each nephron this region of tubule makes close contact with its afferent arteriole
What molecule cuases the vaso constriction in the tubuloglomerular feedback system?
adenosine -
adenosine diffuses to afferent arteriole, adenosine causes afferent arteriolar constriction, RBF and GFR return to normal
What is the reason for maintaining RBF constant within the MAP range?
it maintains the glomerular filtration rate because the glomerular blood flow is directly related to the rate of filtration
What is the advantage of autoregulating GFR and RBF over the range of 90-180 mmHg?
it ensures that the small fluctuations in blood pressure do not result in corresponding fluctuations in RBF and therefore in GFR
*fluctuations in GFR would interfere with the kidney’s ability to balance salt and water excretion with salt and water intake
Do RBF and GFR ever change?
Yes
they change as a result of extrinsic control mechansims mediated by nerves and hormnes
How does nervous control effect RBF and GFR?
the interlobular arteries and the afferent/efferent arterioles are richly innervated by sympathetic fibers - which can cause contraction of the smooth muscle in vessel walls
how do hormones effect the RBF and GFR?
the vascular smooth muscle in the walls of the interlobular arteries and the afferent/efferent arterioles is sensitive to certain circulating compounds
- adrenaline and angiotensin2 cause vasoconstriction
- vascular smooth muscle contraction
- vessel constriction
what hormone causes vasodilation in the kidney?
Bradykinin
What is the SNS activity in the renal vessels of a person at rest with normal circulating blood volume?
activity in SNS fibers = zero
What is the effect of severe exercise, pain, severe emotional stimuli on RBF and GFR?
RBF and GFR are decreased- the decreased renal profusion could potentially lead to kidney failure
What is the effect of a crisis situation e.g. haemorrhage on RBF and GFR?
high degree of sympathetic NS activity may be detected in renal vessels. Also, adrenaline is released and circulating levels of angiotensin 2 increase therefore RBF and GFR decrease
Could decreased RBF after haemorrhage result in renal ischaemia?
prostaglandins (PGE1 and PGE2) both dampen the vasoconstrictor effects on the afferent arterioles of SNS and angiotensin 2
balance between PG activity and that of SNS and angiotensin 2 will determine the extent of decrease in RBF, therefore it could potentially lead ot renal ischaemia … but only if the balance between the two is thrown
